1. Field of the Invention
This invention relates to a bonding method of small parts such as LSI or like semiconductor parts, semiconductor devices and IC chips serving as elemental parts of a micromachine, and a module of combined small parts formed by bonding these small parts together.
2. Description of the Related Art
A machine of mm order such as a micromachine composed of a plurality of small parts has been developed. The small parts include IC chips or the like, for instance, and the machine such as the micromachine is assembled by bonding the IC chips together.
The problems arising when bonding the IC chips together are positioning accuracy of small parts to be bonded together, dimensional dispersion caused by the film thickness of an adhesive applied between the small parts and the deficiency in bonding strength resulting from insufficient bonding area.
As a method for obtaing a sufficient bonding strength in bonding small parts together, a hydrogen-bond applied technique is known, in which silicon wafers, each having a bonding surface subjected to surface hydrophilic treatment (absorption of OH group) is treated with heat of a temperature of not less than 1000xc2x0 C. under no pressure to form a surface oxidized layer, and the silicon wafers are bonded together through the surface oxidized layers. However, since the bonding has to be made under the extreme environment, it is difficult to use an equipment for positioning of the parts, thereby causing problems such that necessary positioning accuracy cannot be assured and that a large-scaled apparatus is needed for heat treatment.
When electrical connections among the small parts such as IC chips are required, an input/output contact of an IC chip molded with epoxy resin is led outside through a lead frame, a leg of the lead frame is mounted on a substrate and this IC chip is connected with another IC chip mounted on the substrate in the same manner through printed wiring on the substrate. Recently, a multi-chip module or the like is known, in which a plurality of chips arranged on an alumina substrate are connected together through thin-film copper wiring of about 20 microns in conductor spacing. However, in either case, the connection between the chips requires the wiring, and this wiring has been a major hindrance to higher speed and higher integration of a circuit.
According to the recent technique, the width or conductor spacing of sub-micron order is practically available for the wiring produced by a semiconductor process in a chip. However, an interface portion required for the electrical connection between the chips, for instance, connecting portions of the leg of the lead frame and the copper wiring, still requires a considerably large contact area as compared with the width or conductor spacing of the wiring produced by the semiconductor process, further hindering to higher integration of the circuit. To be more specific, the spacing between contacts is about 200 microns with the wiring width of 30 microns in the case where contact connection of wire bonding type is applied, while the spacing between contacts is about 80 microns with the wiring width of 30 microns in the case where contact connection of flip chip bonding type is applied.
According, it is an object of the present invention to provide a bonding method of small parts and a module of combined small parts formed by bonding the small parts together, wherein slight bonding areas on the small parts suffice to exert a satisfactory bonding strength without need of any adhesive, complicated chemical processing and heat treatments, but the small parts can be bonded together with high positioning accuracy to obtain a circuit of higher speed and higher integration. Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
According to the present invention, a first small part and a second small part are bonded together by means of one or two or more V-shaped grooves formed on a bonding surface of the first small part, and grooves V-shaped elongate projections, which are engageable with the V-shaped grooves, on a bonding surface of the second small part, thereby fitting the V-shaped elongate projections of the second small part to the V-shaped grooves of the first small part.
According to the present invention, the small parts can be bonded together with a sufficient strength without requiring any adhesive, complicated chemical processing and heat treatments, and the degree of the strength of the bonded state of the small parts can be determined selectively at will if occasion demands. Moreover, since the elongate projection and the tapered groove are joined by being fitted with each other, the positioning accuracy in bonding the small parts together can also be assured.
Further, since the tapered groove and the elongate projection serving as bonding portions of the small parts are provided with electrical contacts for transfer of signals between the objects to be bonded together to electrically connect the small parts together, any intermediate connecting mechanisms such as a lead frame, printed wiring and copper wiring becomes unnecessary, thereby making it possible not only to obtain a circuit of higher speed, but also to prevent the inevitable increase in the size of the node at a portion of connection between the contact and the wiring, contributing to higher integration of the circuit too.